<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <!--<link rel="stylesheet" href="">-->
  <style>
    *{
      margin: 0;
      padding: 0;

      
    }
    .center{
      height: 100px;
      width: 100%;
      float: left;
      background-color: red;
    }
    .right{
      width: 100px;
      height: 100px;
      background-color: blue;
      float: left;
      margin-left: -100px;
    }
    .left{
      height: 100px;
      width: 100px;
      background-color: chartreuse;
      float: left;
      margin-left: -100%;
    }
    p{
      padding: 0 100px;
    }
  </style>
</head>
<body>
  <div class="content">
    <div class="center">
      <p>12</p>
    </div>
    <div class="left"></div>
    <div class="right"></div>
  </div>
</body>
</html>